Why islamists straight away deny comments against mohammed and ask for proof ?

to muslims, mohammad is as pure and flawless as jesus is to christians.... we beleive all his wars were for a holly cause and were chosen with great wisdom.... it is also stated in the quoran that those who die by mistake in a struggle to defeat evil, even when considered on evil's side, go to heaven... some muslims are a bit too touchy about comments against him, but i for one beleive that it is really necessary to discuss such events in history...